Method for real-time adjustment of a planisher

ABSTRACT

A method for real-time adjustment of a planisher for planishing metal strip. After a planished strip has been cut into a plate, the method includes measuring the plate at the output of the planisher outside a support zone, correcting the measurement so as to eliminate the influence due to self-weight of the plate, and correcting, as the case may be, the clamping of rollers located at the planer output so as to obtain a plate with a controlled curve.

The present invention relates to a method for adjusting in real time aplanisher which is to planish metal strips in reel form or in coil form,such as steel strips, or, directly, plates or sheets.

The invention is applicable, on the one hand, to the planishing of metalstrips that are to be cut at the outlet of the planisher in order toobtain plates or sheets of a determined length L and, on the other hand,to the planishing of plates or sheets.

A metal strip or a plate undergoes various operations, such ashot-rolling or cold-rolling, that are intended to confer on ithomogeneous dimensional characteristics over its entire length; thus, arolled metal strip theoretically has a constant thickness and widththroughout.

However, the operation of rolling is not sufficient to obtain a stripfree from defects. The strip may exhibit flatness defects, such asundulations at the edges or the centre, and a bend (that is to say, acurvature) over the length or width of the strip.

These flatness defects are corrected by planishing the strip in aplanisher. Such a planisher is constituted by two stacked cassettes eachsupporting several motorised rollers which are offset relative to oneanother and arranged alternately above and below the path of the strip.In the case of a reel of metal strip, the strip is first of all unwoundfrom the reel and generally straightened in a straightening devicebefore undergoing the planishing operation. In order to supply productsmeeting the flatness criteria required by manufacturers, the planishedstrips are not rewound onto reels, because winding onto reels destroysthe flatness. They are therefore cut at the outlet of the planisher insuch a manner as to obtain plates, sheets or blanks, either by means ofguillotine shears or by means of follower, rotary or flying shears. Theplanished plates or sheets are then transported to a stacker and arestacked while awaiting delivery.

The planishing proper is effected by passing the strip or the platebetween the offset rollers of the planisher, the clamping of whichrollers at the inlet, that is to say, the spacing of the upstreamrollers of the planisher, and at the outlet, that is to say, the spacingof the downstream rollers of the planisher, is adjusted. At the inlet ofthe planisher the residual stresses of the strip are homogenised and theflatness defects, such as undulations and bending over the width, arethus remedied. At the outlet of the planisher, the bending over thelength of the strip is treated. For greater clarity in the rest of thetext, simply the word “bend” will be used to mean “bend over thelength”.

The adjustment of the clamping parameters at the inlet and the outlet ofthe planisher is effected each time a reel, plate (or sheet) is changed,in order to adapt those parameters not only to the dimensionalcharacteristics and to the types of defect of the strip or the plate butalso as a function of the bend, depending on the form which it isdesired to impart to the plate (or the sheet) after planishing.

Depending on the purpose for which the manufacturers intend to use theplanished plates (or sheets), or depending on the type of installationwhich those manufacturers possess, the plates are delivered with a zerobend (absolutely flat plate), a positive bend or a negative bend.

First of all, the clamping of the inlet rollers of the planisher isadjusted in accordance with methods known per se, and then the clampingof the outlet rollers is adjusted.

A known means of adjusting the outlet rollers of the planisher consistsin checking the residual bend of the plate (or sheet) after planishing.For that purpose, the plate is lifted by means of a lifting device insuch a manner that the plate is suspended by one or two support points,and then an operator measures the bend of the plate by determining thepitch at the centre of the plate by means of a ruler. The operator canthen adjust the setting of the clamping of the rollers at the outlet inorder to correct the bend of the plate and to adapt it to themanufacturer's requirements. This measuring operation is repeated asmany times as necessary at each change of product (in the form of areel, plate or sheet).

That technique has the following various disadvantages:

-   -   measurement of the bend of a plate at the change of a product        and the adaptation of the clamping of the outlet rollers by the        operator makes it necessary to stop the planishing line during        that operation, which leads to a loss in productivity;    -   some planishing lines are compact, and it is not always possible        to install a device for lifting the plates; in that case the        bend of the plate is measured away from the line with an even        greater line stoppage time;    -   the operation of lifting the plate may comprise safety risks for        the operator, especially in the case of large plates (more than        2 m in length).

In addition, although the dimensional characteristics of a strip of agiven reel are constant over its entire length, the same is not true ofthe mechanical characteristics. The variations in the mechanicalcharacteristics of a strip have a negative impact on the control of thefinal bend of the plates after the strip has been planished. Since theclamping of the rollers at the outlet of the planisher has been adjustedfor a given mechanical characteristic of the strip, that clamping, inthe course of the planishing operation, will no longer be suitable ifthe mechanical characteristics of the strip vary to a considerableextent.

The control of the residual bend of the plate is an important operationto the extent that the tolerances required by manufacturers in relationto the dimensions and the bend of the plate are becoming increasinglynarrow. By way of example, at present, tolerances in relation to thebend of plates intended for LASER cutting, and for some motor vehicleapplications, such as connecting pieces, are often less than ±3 mm/m.The object of the present invention is to overcome the disadvantages ofthe method used in the prior art.

The invention therefore relates to a method for adjusting in real time aplanisher that is to planish metal strips, plates or sheets,characterised in that:

-   -   after the strip has been planished, it is cut to obtain a plate        or a sheet;    -   the curvature of the plate resulting either from the planishing        of the cut strip or from the planishing of the plate is measured        at the outlet of the planisher outside a support region;    -   the measurement is corrected in such a manner as to eliminate        the influence attributable to the dead weight of the plate; and    -   if necessary, the clamping of the rollers located at the outlet        of the planisher is corrected in such a manner as to obtain a        plate having a controlled bend.

According to other preferred features of the invention:

-   -   the measurement of the residual bend of the planished plate is        effected on the basis of a measurement of the curvature of the        plate at the outlet of the planisher outside the support region,        the measurement being effected by means of at least three        distance sensors;    -   the measurement of the residual bend of the planished plate is        deduced from the measured curvature and the inherent curvature        of the planished plate.

The invention relates also to a planishing installation of the typecomprising a planisher for planishing metal strips, plates or sheets,characterised in that it comprises means for cutting the strip, afterplanishing, into planished plates or into planished sheets, means formeasuring the residual bend of the planished plates or planished sheetsresulting either from the planishing of the cut strip or from theplanishing of the plate or the sheet, at the outlet of the planisher,and means for modifying the clamping of the rollers located at theoutlet of the planisher as a function of the information provided by themeans for measuring the residual bend.

According to other features of the invention:

-   -   the means for measuring the residual bend comprise at least        three distance sensors, such as optical distance sensors, or        eddy current distance sensors;    -   the planishing installation comprises automatic means for        adjusting the clamping of the outlet rollers as a function of        the information provided by the distance measurements of the        sensors;    -   the curvature of the planished plate is measured at the said        planished plate outside a support region.

As will have been appreciated, the invention consists in performing ameasurement in real time of the bend of the plate or of the strip cut toform a plate on leaving the planisher, and in regulating the clamping ofthe rollers as a function of the results of that measurement.

The features and advantages of the invention will emerge on reading thefollowing description which is given by way of example and withreference to the appended drawings in which:

FIG. 1 is a diagrammatic view in cross-section of a planisher;

FIG. 2 shows the variation in the value of the residual bend as afunction of the clamping of the rollers at the outlet of the planisher.

FIG. 1 shows diagrammatically a planisher 1 comprising two stackedcassettes 2, 3 supporting motorised rollers 4 which are positioned in anoffset manner relative to one another and between which a metal strip 5,a plate or a sheet passes. The installation comprises cutting means 6located at the outlet of the planisher, a transport table 7, a means forconveying the strip cut into plates (which means is not shown in theFigure). In the case of planishing strips, the installation comprisescutting means 6 located at the outlet of the planisher. Of course, thecutting means 6 are superfluous when plates or sheets are beingplanished directly; however, they may be present in the installation andin that case they are not caused to operate. Shown at 8 is the plate orthe sheet (resulting either from the shearing of the strip afterplanishing or from the planished plate or sheet), one portion of whichis supported on the table 7 and the other portion of which projectsbeyond the table 7. Distance sensors placed, in our diagram, below theregion of the planished plate 8 not supported by the table 7, areconnected to a system 11 for adjusting the clamping of the rollers 4 aand 4 b located at the outlet of the planisher, which system is itselfconnected to an actuator 12 for regulating the clamping at the outlet(rollers 4 a and 4 b).

The metal plate or strip 5 is planished in the planisher 1 by passingbetween the rollers 4. At the outlet of the planisher, the strip 5 issheared by the cutting means 6, which are constituted either byguillotine shears or by rotary, follower or flying shears, in such amanner as to obtain plates 8, sheets or blanks having a length Ldetermined in advance. One portion of the planished plate 8 rests on thetransport table 7 while a length of plate L′ determined in advance by adetection cell 10 projects beyond the table 7 and is therefore locatedoutside the support region.

At least three sensors 9 located on a reference base (not shown in theFigure) positioned either above or below the region corresponding to thelength L′ of the plate 8 measure the distance that separates them fromthe portion of the plate 8 of length L′ in order to determine thecurvature C thereof. The measurements performed by the sensors 9 arepreferably contactless distance measurements in order to avoidfalsifying the measurements of the curvature of the portion of the plate8 of length L′. Use will therefore be made of contactless distancesensors 9, such as eddy current sensors or optical sensors . . .

In order to determine the residual bend C_(r) of the plate 8 on thebasis of the measured curvature C, it is expedient to take into accountthe curvature C_(p) of the plate 8 that is due to its dead weight.Knowledge of the following parameters:

-   -   length L′ of the plate 8 that projects beyond the table 7,        determined by a position cell 10,    -   thickness of the plate 8,    -   spacing of the sensors 9 from the table 7,        enables the curvature C_(p) of the plate 8 that is due to its        dead weight to be calculated.

Thus, by subtracting the value of the curvature C_(p) from the value ofthe measured curvature C, the residual bend C_(r) of the plate 8 iseasily obtained.

Knowing the residual bend C_(r) of the plate 8, the transfer function iscalculated, which then enables the clamping at the outlet (rollers 4 aand 4 b) of the planisher 1 to be adjusted in such a manner as to adaptthe bend of the following plate 8 to the manufacturer's requirements.

The bend of the plate 8 required by the manufacturer may be zero(absolutely flat plate), positive (upward curvature of the plate) ornegative (downward curvature of the plate). In order to obtain plateshaving one of those profiles, it is expedient either to increase or todecrease the spacing of the rollers 4 a relative to the rollers 4 blocated at the outlet of the planisher 1.

That operation may be effected by an operator who gathers the variousmeasurements mentioned above and uses those measurements to calculatethe transfer function permitting deduction of the clamping parameters,at the outlet, of the rollers 4 a and 4 b, which parameters are to beintroduced into the adjusting system 11 in accordance with the bend thatit is desired to apply to the plate.

That operation may also be effected automatically by a computer.

As soon as the clamping parameters of the rollers 4 a and 4 b have beendetermined, the actuator 12 acts directly on the clamping of the rollers4 a and 4 b at the outlet of the planisher 1, that is to say, on theirrelative spacing.

The method according to the invention thus permits real-time control ofthe bend of each of the plates 8. Thus, when the mechanicalcharacteristics of the plate 8 of a reel vary, the real-time control ofthe bend of the plate 8 makes it possible to act immediately on theclamping parameters at the outlet of the planisher 1 and, if necessary,to modify the clamping adjustments at the outlet (rollers 4 a and 4 b)in such a manner as to obtain plates 8, the bend of which is constant orthe value of the bend of which remains within the limits of thetolerance set by the manufacturer.

Apart from the advantage mentioned above, the method according to theinvention does away with the operations of lifting the plate andmeasuring the bend by an operator and has the following additionaladvantages over the prior art:

-   -   improvement in safety conditions;    -   elimination of the time spent on handling the plates, thus        permitting an increase in the overall productivity of the line;    -   rapidity of performing the corrections to the clamping of the        rollers, in the case where an automatic computer is used;    -   operation for controlling the bend of the plate easy to        implement, no restriction to plates of a length less than 3 m        for thicknesses of 3 mm as was the case with the method of the        prior art;    -   gain in space: the device according to the invention is        compatible with compact lines and it requires less space than        that necessitated by the lifting of the plate;    -   systematic control of the bend of all the plates (archiving of        values).

FIG. 2 shows the variation in the value of the residual bend (expressedin mm/m) as a function of the clamping of the rollers at the outlet ofthe planisher (expressed in mm).

The material under consideration is a steel strip which is 6 mm thickand 1500 mm wide and which has an elastic limit of 350 Mpa. The initialrate of plasticisation of the strip is 60%. The maximum rate ofplasticisation intended for this example is 80%. This set rate ofplasticisation depends on the planishing strategy used and on theinitial flatness of the strip before planishing. The range of variationin the bend after planishing is directly correlated with that parameter.

The aim of the following Examples is to illustrate the use of themethod.

In Example 1, the contactless distance sensors measure a residual bendof the plate obtained after planishing and shearing the steel strip of+7 mm/m. In order to render the bend of this plate zero (absolutely flatplate), it is necessary for the adjusting system (a) to correct theclamping of the rollers at the outlet of the planisher by a correctionof 0.15 mm so that the clamping reaches 0.32 mm.

In Example 2, the contactless distance sensors measure a residual bendof the plate obtained after planishing and shearing the steel strip of−7 mm/m. In order to render the bend of this plate zero (absolutely flatplate), it is necessary for the adjusting system (a′) to correct theclamping of the rollers at the outlet of the planisher by a correctionof 0.2 mm so that the clamping reaches 0.32 mm.

1. A method for adjusting in real time a planisher that is to planishmetal strips, plates or sheets, the method comprising: planishing ametal strip and then cutting the metal strip to obtain a planishedplate; measuring, at an outlet of the planisher at an unsupported regionof the planished plate, a curvature of the planished plate; correctingthe measurement to eliminate an influence attributable to a dead weightof the planished plate; and adjusting the clamping of rollers located atthe outlet of the planisher based upon the measurement to obtain aplanished plate having a controlled bend.
 2. The method according toclaim 1, further comprising determining a residual bend of the planishedplate based on the measurement of the curvature of the planished platethe measurement of the curvature of the planished plate being effectedby means of at least three distance sensors.
 3. The method according toclaim 1, wherein a residual bend of the planished plate is deduced fromthe measured curvature of the planished plate and an inherent curvatureof the planished plate.
 4. A planishing installation of the typecomprising a planisher for planishing metal strips, plates or sheets,the planishing installation comprising: means for cutting a metal strip,after planishing the metal strip, into planished plates or planishedsheets; means for measuring a residual bend of the planished plates orthe planished sheets, at an outlet of the planisher; and means formodifying the clamping of rollers located at the outlet of theplanisher, as a function of information provided by the means formeasuring the residual bend, wherein the curvature of the planishedplates or the planished sheets is measured at an unsupported region ofthe planished plates or the planished sheets.
 5. The planishinginstallation according to claim 4, wherein the means for measuring theresidual bend comprises at least three distance sensors.
 6. Theplanishing installation according to claim 5, wherein the means formeasuring the residual bend comprises at least three optical distancesensors.
 7. The planishing installation according to claim 5, whereinthe means for measuring the residual bend comprises at least three eddycurrent distance sensors.
 8. The planishing installation according toclaim 5, further comprising means for automatically adjusting theclamping of the outlet rollers, as a function of the informationprovided by the distance measurements of the distance sensors.